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2012年新GRE数学考点指导——Combinations

2012-11-04 来源:读书人 

  Combinations of Choices

  If there are n choices for one type and m choices for second type, then number of combinations for both types is the product of choices:n*m.

  Example:

  If there are 3 kinds of breads to choose from and 4 kinds of meats, then we can make 3*4=12 different sandwiches.

  If an alphabet has 26 letters, then the number of possible 2 letter word is 26*26=676.All of them may not be vaild words.

  Remember:

  Do not add the choices to get the total combinations.

  The product rule can be applied to more than two types of choices: if there are 3 kinds of breads, 4 kinds of meats, and 6 kinds of cheeses, then we can make 3*4*6=72 different sandwiches.


(作者:读书人网友 编辑:kind887)
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